Robert Aymar, the Director General of CERN, has announced that the LHC will operate when it starts up this year at an energy of 5 TeV per beam (10 TeV total center of mass energy), rather than the design energy of 7 TeV per beam. To operate the LHC magnets at the highest current and get to 7 TeV requires a time-consuming sequence of powering tests and quenches, so the decision was made to put this off until the winter shutdown. With this decision, the process of beam commissioning can start soon after all sectors have been cooled down, and this is now scheduled for mid-June. Beam commissioning should take two months, with first physics collisions thus scheduled for late summer.
It remains possible that problems will be found during or after cooldown that will require warming back up one or more sectors, and this would lead to a delay of a couple months or so. The last sector scheduled to be cooled down is 4-5, which is now warm to allow repair of the defective triplet magnets. Whenever a sector is warmed up, a major problem is damage to defective PIMs which then need to be replaced. If there are too many of these, a delay in the cooldown is possible. The search for damaged PIMs relies on a “sputnik” tennis-ball-like sensor sent through the beam-pipe. Latest news is that 4 damaged PIMS have been found so far.
Update: I’d been wondering how much extra work this change in energy would cause for the experimentalists, just saw a posting about this by Gordon Watts, entitled Start Your Monte-Carlo Engines!
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